Gold(III) π‐Allyl Complexes

Gold(III) π‐complexes have been authenticated recently with alkenes, alkynes, and arenes. The key importance of Pd^II π‐allyl complexes in organometallic chemistry (Tsuji–Trost reaction) prompted us to explore gold(III) π‐allyl complexes, which have remained elusive so far. The (P,C)Au^III(allyl) and (methallyl) complexes 3 and 3′ were readily prepared and isolated as thermally and air‐stable solids. Spectroscopic and crystallographic analyses combined with detailed DFT calculations support tight quasi‐symmetric η³‐coordination of the allyl moiety. The π‐allyl gold(III) complexes are activated towards nucleophilic additions, as substantiated with β‐diketo enolates.     

Comprehensive and quantitative stability study of ascorbic acid using capillary zone electrophoresis with ultraviolet detection and high‐resolution tandem mass spectrometry

Ascorbic acid is a powerful antioxidant compound involved in many biological functions, and a chronic deficiency is at the origin of scurvy disease. A simple, rapid, and cost‐effective capillary electrophoresis method was developed for the separation and simultaneous quantification of ascorbic acid and the major degradation products: dehydroascorbic acid, furfural, and furoic acid. Systematic optimization of the conditions was performed that enabled baseline separation of the compounds in less than 10 min. In addition to simultaneous quantification of ascorbic acid alongside to the degradation products, stability studies demonstrated the possibility using capillary electrophoresis to separate and identify the major degradation products. Thus, high‐resolution tandem mass spectrometry experiments were conducted in order to identify an unknown degradation product separated by capillary electrophoresis and significantly present in degraded samples. Comparison of mass spectrometry data and capillary electrophoresis electropherograms allowed to identify unambiguously trihydroxy‐keto‐valeraldehyde. Finally, capillary electrophoresis was successfully applied to evaluate the composition of different pharmaceutical preparation of ascorbic acid. Results showed the excellent performance of the capillary electrophoresis method due to the separation of excipients from the compounds of interest, which demonstrated the relevance of using an electrophoretic separation in order to perform comprehensive stability studies of ascorbic acid.     

Synthesis of a Stable N-Hetero-RhI-Metallacyclic Silanone

A novel N-hetero-Rh^I-metallacyclic silanone 2 has been synthesized. The silanone 2 , showing an extremely large dimerization energy (ΔG=+86.2 kcal mol⁻¹), displays considerable stability and persists in solution up to 60 °C. Above 120 °C, an intramolecular C_sp3−H insertion occurs slowly over a period of two weeks leading to the bicyclic silanol 5 . The exceptional stability of 2 , related to the unusual electronic and steric effects of Rh^I-substituent, should allow for a more profound study and understanding of these new species. Furthermore, the metallacyclic silanone 2 presents two reactive centers (Si=O and Rh), which can be involved depending upon the nature of reagents. Of particular interest, the reaction with H₂ starts with the hydrogenation of Rh^I center leading to the corresponding Rh^III-dihydride complex 7 and it undergoes a cis/trans-isomerization via a particular mechanism, demonstrating that addition-elimination processes can also happen for silanones just like for their carbon analogues!     

Characterization of defects in GaP and GaAsP graded heterojunctions by transmission electron microscopy

Misfit dislocations are observed in graded heterojunctions GaAs_1?xP_x by electron microscopy. Results are in agreement with previous work concerning the nature of the dislocations (Lomer and 60° dislocations) and their density dependence on the phosphorus gradient. The discussion concerns the formation of Lomer dislocations and the possibility of reducing the density of inclined dislocations which reach the surface of the epitaxial layer. GaP substrates, S-doped, are examined by transmission electron microscopy. Numerous defects such as Frank loops, perfect loops, helical dislocations and precipitates are observed. A GaP homoepitaxial layer realized on this substrate is free from these defects but exhibits stacking faults. A zinc diffusion does not produce additional defect but a 1000 Å thick amorphous layer is observed a at the surface.     

VUV photochemistry simulation of planetary upper atmosphere using synchrotron radiation

The coupling of a gas reactor, named APSIS, with a vacuum‐ultraviolet (VUV) beamline at the SOLEIL synchrotron radiation facility, for a photochemistry study of gas mixtures, is reported. The reactor may be irradiated windowless with gas pressures up to hundreds of millibar, and thus allows the effect of energetic photons below 100 nm wavelength to be studied on possibly dense media. This set‐up is perfectly suited to atmospheric photochemistry investigations, as illustrated by a preliminary report of a simulation of the upper atmospheric photochemistry of Titan, the largest satellite of Saturn. Titan's atmosphere is mainly composed of molecular nitrogen and methane. Solar VUV irradiation with wavelengths no longer than 100 nm on the top of the atmosphere enables the dissociation and ionization of nitrogen, involving a nitrogen chemistry specific to nitrogen‐rich upper atmospheres.     

Fundamental analysis of defects induced by energetic ions implantation in AgCl

The effects of the energetic ions implantation in AgCl can be related to two types of perturbation due to: the electronic energy losses observed, essentially with H⁺ (2 MeV) implantation and the collision energy losses illustrated in K⁺ (0.5 MeV) implantation.

The ionization influence is essentially the sensibilization of AgCl (print-out) at RT and at LNT. We discuss the the photolysis mechanism regarding the one postulated under action of light.

The defects related to collision losses are characterized by a new optical absorption band with a characteristic length independent of the implanted ion (Na⁺ and K⁺). The nature of those defects are analysed by thermal and optical bleaching and by EPR. Those collision effects do not contribute to the print-out phenomena.     

Synthesis of stable free base secochlorins and their corresponding metal complexes from meso-tetraarylporphyrin derivatives

Cleavage reactions of 2,3-diamino-meso-tetraarylporphyrins and meso-tetraarylporphyrins fused to imidazole rings afforded secochlorins including stable free base derivatives.     

A Robust Infinite Zirconium Phenolate Building Unit to Enhance the Chemical Stability of Zr MOFs

A novel Zr‐chain based MOF, namely MIL‐163, was designed and successfully synthesized using a bis‐1,2,3‐trioxobenzene ligand. Endowed with large square‐shaped channels of 12 Å width, it shows remarkable water uptake (ca. 0.6 cm³ g^?1 at saturating vapor pressure) and a remarkable stability in simulated physiological media, where archetypical Zr carboxylate MOFs readily degrade.     

Fluorescently Labeled Substrates for Monitoring α1,3‐Fucosyltransferase IX Activity

Fucosylation is often the final process in glycan biosynthesis. The resulting glycans are involved in a variety of biological processes, such as cell adhesion, inflammation, or tumor metastasis. Fucosyltransferases catalyze the transfer of fucose residues from the activated donor molecule GDP‐β‐L ‐fucose to various acceptor molecules. However, detailed information about the reaction processes is still lacking for most fucosyltransferases. In this work we have monitored α1,3‐fucosyltransferase activity. For both donor and acceptor substrates, the introduction of a fluorescent ATTO dye was the last step in the synthesis. The subsequent conversion of these substrates into fluorescently labeled products by α1,3‐fucosyltransferases was examined by high‐performance thin‐layer chromatography coupled with mass spectrometry as well as dual‐color fluorescence cross‐correlation spectroscopy, which revealed that both fluorescently labeled donor GDP‐β‐L ‐fucose‐ATTO 550 and acceptor N‐acetyllactosamine‐ATTO 647N were accepted by recombinant human fucosyltransferase IX and Helicobacter pylori α1,3‐fucosyltransferase, respectively. Analysis by fluorescence cross‐correlation spectroscopy allowed a quick and versatile estimation of the progress of the enzymatic reaction and therefore this method can be used as an alternative method for investigating fucosyltransferase reactions.